After earning his degree in economics, Miller worked for the War Labor Board during World War II. In 1950, he became staff economist of the United Steel Workers Union. He worked his way up to the chief research director of the USWA and assistant to the president. When questioned as to his involvement in the previously-weak MLBPA given his powerful role with the steelworkers union, Miller explained that he grew up near Ebbets Field as a Brooklyn Dodgers fan and wanted to advocate for the players in the game he loved.

After stepping down as the head of the MLBPA, Miller consulted with the union for several years and worked during the 1990 lockout. He is the author of A Whole Different Ballgame (1991).

Miller has been a leading candidate to be elected to the Hall of Fame as an executive since his retirement from the Players' union. He seemed on the verge of election when the Veterans Committee was reformed following the controversial election of Bill Mazeroski in 2001. At first, he received little consideration from the new Veterans Committee and claimed that this was because the committee was now largely constituted of representatives from management who still bore him a grudge in the vote taking place in 2007. A number of former players now in the Hall rallied to his cause, led by Tom Seaver and Joe Morgan. In the 2010 vote, he fell just shy of election, missing by one vote.

After asking that his name be taken off the ballot after his failure to be elected in 2007, something which the Hall of Fame declined to do, he issued a very bitter statement after missing out in 2010: "The Baseball Hall of Fame's vote (or non-vote) of December 5, hardly qualifies as a news story. It is repetitively negative, easy to forecast, and therefore boring. A long time ago, it became apparent that the Hall sought to bury me long before my time, as a metaphor for burying the union and eradicating its real influence. Its failure is exemplified by the fact that I and the union of players have received far more support, publicity, and appreciation from countless fans, former players, writers, scholars, experts in labor management relations, than if the Hall had not embarked on its futile and fraudulent attempt to rewrite history. It is an amusing anomaly that the Hall of Fame has made me famous by keeping me out."

Given the history of the institution, it is almost certain that Miller will be elected eventually, although the honor will have to come posthumously.

"Marvin Miller was a highly accomplished executive and a very influential figure in baseball history. He made a distinct impact on this sport, which is reflected in the state of the game today, and surely the Major League players of the last half-century have greatly benefited from his contributions."

On January 21, 2013, a number of former players and MLB executives organized a memorial tribute in his honor at his alma mater, New York University's School of Law, in anticipation of his name being up again for consideration by the Veterans Committee at the end of the year. Hall of Fame players such as Dave Winfield and Reggie Jackson, and non Hall of Famers such as Jim Bouton, Buck Martinez and Keith Hernandez paid tribute to Miller's work. In an indication that the bitterness was finally starting to ease, representatives of the Commissioner's office such as MLB Vice-Presidents Katy Feeney and Rob Manfred were also present for the lavish event.